Coil for electric rotating machine, and mica tape and mica sheet used for the coil insulation

ABSTRACT

A coil for an electric rotating machine is configured with a conductor which is formed by bundling a plurality of square strands and stacking the square strands like a coil with Roebel transposition, mica tape which is wound a plurality of layers around an outer surface of the conductor and made up of mica paper and glass cloth backing, and an insulation wall formed by impregnating and curing resin between wound layers of the mica tape. Inorganic particles are supported with the glass cloth backing on the mica tape using an adhesive containing glue insoluble in the impregnated resin as an indispensable component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/690,644, filed on Oct. 23, 2003, which is a Continuation Applicationof PCT Application No. PCT/JP02/04033, filed Apr. 23, 2002, which wasnot published under PCT Article 21(2) in English. This application isbased upon and claims the benefit of priority from the prior JapanesePatent Application No. 2001-132940, filed Apr. 27, 2001, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coil for an electric rotatingmachine, which is configured by forming an insulation layer on theperiphery of a conductor, and mica tape and a mica sheet used for thecoil insulation.

2. Description of the Related Art

In a stator of a high-voltage electric rotating machine such as agenerator and a motor, as shown in FIG. 1, a plurality of slots 1 a areformed on the inner surface of stator core 1. The each slot 1 aaccommodates a stator coils 2.

The stator coils 2 comprise an upper coil and a lower coil. Toaccommodate the upper and lower coils into the slot, insulation spacers3 are inserted into the bottom of the slot 1 a, between the upper andlower coils, and into the opening of the slot 1 a.

Furthermore, a slot wedge 4 for securing the stator coil 2 is insertedin the open end of the slot 1 a. The slot wedge 4 suppresses the statorcoil 2 vibration generated from electromagnetic pulsating force due toload current in the conductor.

In the above stator of the high-voltage electric rotating machine, thestator coil 2 accommodated in the slot 1 a of the stator core 1 isformed of a conductor that has the following structure.

First, a plurality of insulated square strands 21 are bundled andRoebel-transposed. After that, pre-preg separator 11 with thermosettingresin is arranged between a strand bundle 30 a on the left side row inthe figure and a strand bundle 30 b on the right side row in the figure.Pre-preg filler 12 with thermosetting resin is arranged on theRoebel-transposed portion on top and bottom of the strand bundles 30 aand 30 b.

Then, the thermosetting resin in the pre-preg separator 11 and that ofthe pre-preg filler 12 are heated and cured while the strand bundles 30a and 30 b are integrally molded in one piece by heat pressing. Aconductor 22 is finished to finally have a section as shown in thefigure by heating and curing the pre-preg separator 11 and pre-pregfiller 12.

The conductor 22 is insulated by the following process called vacuumpressurized impregnation system with thermosetting resin.

A mica tape 7, which includes mica paper 5 and glass cloth backing 6 asshown in FIG. 2, is wound a plurality of layers around the conductor 22.Thermosetting resin is impregnated into the wound layers of the micatape 7 under vacuum pressurized condition. After that, the thermosettingresin and the mica tape 7 are heated and cured by heat pressing whilethe stator coil 2 is molded to so as to have a final section. Aninsulation layer 8 is formed on the periphery of the conductor 22 byheating and curing the thermosetting resin and the mica tape 7.

In the stator coil 2 so configured, the conductor 22 generates heat byload current at the time of the operation of the electric rotatingmachine. Part of the generated heat is transmitted to the environmentalcooling gas directly from ventilation ducts, which are arranged on thecross section of the stator core 1 at appropriate intervals in the axialdirection, through the insulation layer 8. Most of the remaininggenerated heat is transmitted to the stator core 1 through theinsulation layer 8 and then indirectly to the environmental cooling gas.When the generated heat is thus transmitted to the cooling gas, all theheat generated from the conductor 22 is cooled via the insulation layer8 of the stator coil 2. From these points of view, the thermalconductivity along the heat passage is very important.

If the thermal resistance along the heat passage is high, the heatgenerated in the conductor 22 will be hard to transmit to the coolinggas and thus the temperature of the stator coil 2 will increase toexcess. The excessive temperature rise accelerates the deterioration ofelectrical and mechanical performance of organic materials in theinsulation layer 8 as the electric rotating machine is operated for along time.

The above insulation layer 8 includes mainly mica paper 5, glass clothbacking 6, thermosetting resin, etc. The thermal conductivity of mica isabout 0.5 W/m·K, that of glass is about 1.0 W/m·K, and that of epoxyresin, which is a typical thermosetting resin, is about 0.2 W/m·K.

In order to improve the thermal conductivity of the insulation layer 8,therefore, it is effective to reduce the volume of thermosetting resinwith the lowest thermal conductivity.

Moreover, the impregnated thermosetting resin can easily be detained inthe texture of the glass cloth backing 6 and in the mica paper 5. Toprevent the thermosetting resin from being detained, the measuresadopting a very thin glass cloth backing 6, squeeze out the impregnatingresin by applying an appropriate molding pressure at the time of heatingand curing, and the like are taken.

The prior art to positively improve the thermal conductivity of theinsulation layer 8 of the stator coil 2 is disclosed in Jpn. Pat. Appln.KOKAI Publication No. 55-53802 (former) and U.S. Pat. No. 4,806,806(latter).

In the former improved art, inorganic particles such as aluminum oxideand boron nitride having higher thermal conductivity than that of theresin are mixed with mica flakes together with synthetic fibers such aspolyamide fibers. The inorganic particles so used each have a diameterof 30 μm to 100 μm. The synthetic fibers serve as a reinforcement memberfor the mixed mica paper.

In the latter improved art, the inorganic particles of high thermalconductivity are arranged not only in the mica paper but also betweenlayers of the mica tape 7.

Specifically, the following techniques are disclosed:

(1) After a mica tape is wound around a conductor, a resin to whichinorganic particles are added is impregnated and then heated and curedin a molding jig.

(2) A so-called pre-preg mica tape that is pre-impregnated with a resincontaining inorganic particles is wound around a conductor and thenheated and cured in a molding jig.

(3) A so-called pre-preg mica tape that is pre-impregnated with a resinis coated with inorganic particles on its surface and wound around aconductor. After that, it is heated and cured in a molding jig.

(4) A thin insulation tape coated with inorganic particles is woundaround a conductor, together with a mica tape, to form a main insulationlayer.

However, there were some problems in taking the conventional measures toimprove the thermal conductivity of the stator coil insulated by theabove-mentioned vacuum pressurized impregnation method.

In the former method of mixing the inorganic particles with the micaflakes, together with the synthetic fibers such as polyamide fibers, theinorganic particles are buried and dispersed in the mica paper. Thus,the inorganic particles and the synthetic fibers make slits in the micapaper.

Consequently, in the impregnation of resin after the winding of micatape around the conductor, the slits formed by the inorganic particlesfacilitate the resin impregnation. On the other hand, the slits formedby the inorganic particles that are present in the insulation layerprovided on the peripheral surface of the conductor decrease theelectrical strength.

In the case of method (1), or in the latter method of adding highthermal-conductivity inorganic particles to the resin and impregnatingresin not only in the mica paper but also between layers of the micatape, the added inorganic particles will precipitate during the storingof the impregnating resin. Moreover, the inorganic particles could bedistributed unevenly as the result of filtering with the mica tape inthe impregnation process.

In the case of method (4), a thin insulation tape coated with inorganicparticles is wound more layers than necessary. Therefore, the increaseof the thickness of the main insulation layer cannot be ignored.

The methods (2) and (3) are so-called pre-preg insulation system using apre-preg mica tape. If these methods were introduced to the vacuumpressurized impregnation system, the following peculiar problems willarise.

In mica tape for the vacuum pressurized impregnation system, the micaflakes are adhered each another, and mica paper and glass cloth backingare also adhered with a minimum amount of adhesive. The adhesive must bedissolved with the impregnating resin during the impregnation processand they must be formed integrally as a main insulation wall throughheat curing. Consequently, the adhesive is required to have mutualdissolubility with the impregnated resin. If, therefore, the impregnatedresin is, for example, epoxy resin including a curing agent, the epoxyresin (which may contain an accelerator) is generally selected as anadhesive.

In order to improve the thermal conductivity with the mica tapeaccording to the methods (2) and (3), retaining the inorganic particlesarranged on the mica tape with a minimum amount of adhesive and forminga main insulation wall through heat curing after the impregnationprocess are required.

However, when the mica tape that holds the inorganic particles with theadhesive is wound around the conductor and then impregnated with resinin the impregnation process, the adhesive and the impregnated resin aredissolved each other and the resin viscosity temporarily decreases atthe early stage of heat curing. For this reason, a part of resinincluding the inorganic particles flows out of the insulation layer.

Particularly, in a system that molds the conductor 22 by heat pressing,the squeeze-out of the inorganic particles increases as a moldingpressure force to squeeze out an excess impregnated resin from theinsulation layer.

The tendency of flow of the inorganic particles is more conspicuous in asystem that is impregnated with a low-viscosity, high-solubility resinand molded at a high pressure.

In an insulation system configured by a vacuum pressurized impregnationsystem as described above, even though a given number of inorganicparticles are added in advance to the mica tape, they will flow outduring the molding. Therefore, the thermal conductivity cannot beimproved as is expected.

BRIEF SUMMARY OF THE INVENTION

A coil for an electric rotating machine, and mica tape and a mica sheetused for the coil insulation are configured as follows.

A coil for an electric rotating machine is configured by bundling aplurality of square strands, stacking the square strands like a coilwith Roebel transposition, winding mica tape which is made up of micapaper and glass cloth backing, a plurality of mica tape layers aroundthe conductor, and impregnating and curing resin between wound layers ofthe mica tape to form an insulation wall. Inorganic particles aresupported by the mica tape using an adhesive containing glue insolublein the impregnated resin as a component.

Mica tape used for a coil insulation of an electric rotating machinecomprises mica paper and glass cloth backing. Inorganic particles aresupported with the glass cloth backing using an adhesive containing glueinsoluble in impregnating resin as an indispensable component.

A mica sheet used for a coil insulation of an electric rotating machinecomprises mica paper and glass cloth backing. Inorganic particles aresupported with the glass cloth backing using an adhesive containing glueinsoluble in impregnating resin as an indispensable component.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional drawing of a stator coil accommodated in a statorcore slot of a high-voltage electric rotating machine.

FIG. 2 is a sectional drawing showing mica tape that makes up aninsulation wall formed on the periphery of a conductor of a conventionalstator coil.

FIG. 3 is a sectional drawing showing mica tape (mica sheet) forexplaining the first to third embodiments.

FIG. 4 is a graph showing measurement results of impregnating time of aninsulation wall according to the first embodiment.

FIG. 5 is a graph showing the weight percentage of inorganic particlesflowing out from the insulation wall according to the first embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be explained below.

In a stator coil of a high-voltage electric rotating machine, a step ofcompletely finishing a conductor having a final section from insulatingsquare strands has already been described in Background Art. Hence, afirst embodiment concerning an insulation wall 8 formed on the peripheryof a conductor 22 will be explained with reference to FIGS. 1, 3, 4 and5.

In the first embodiment, uncalcinated muscovite mica tape 71 having astructure as shown in FIG. 3 is wound a plurality of layers around theconductor 22. The uncalcinated muscovite mica tape 71 comprises micapaper 5 and glass cloth backing 6. Inorganic particles 14 are supportedwith the glass cloth backing 6 of the mica tape 71 using an adhesive 13.

The adhesive 13 contains glue that is insoluble in impregnating resin asan indispensable component. Favorably, an adhesive 13 containing 4 wt %of polyvinyl alcohol is used as a polyvinyl-based polymer that producesthe effect of supporting the inorganic particles 14. Favorably, 30 wt %of aluminum oxide particles of mica tape are used as the inorganicparticles 14.

As the adhesive 13, an epoxy resin composition (for example, Epikote 828or 1001 manufactured by Yuka-Shell Co., Ltd.) is used in addition to thepolyvinyl alcohol.

After a thermosetting resin is impregnated into the mica tape layers 71under vacuum pressurized condition, it is heated and cured by heatpressing at a pressure of 0.5 MPa while the insulation layer 8 is formedso as to have a final section.

The impregnating resin is, for example, a composition comprising a 45 wt% of cycloaliphatic epoxy compound, a 45 wt % of acid anhydride curingagent, and a 10 wt % of reactive diluent. This impregnating resin has alow viscosity of about 40 mPa·s at room temperature.

For a try, the uncalcinated muscovite mica tape 71 of the presentembodiment, in which only the additional amount of polyvinyl alcohol ischanged, is wound a plurality of layers around the conductor 22 to forman insulation wall 8 having a final thickness of, e.g., 5 mm. Theconductor 22 on which the insulation layer 8 is formed with the micatape 71 is submerged in the impregnating resin and applied a pressureof, e.g., 0.7 MPa in the tank after vacuum treatment.

The time that lapses until the completion of resin impregnation and theweight of inorganic particles in the resin squeezed out at molding withheat pressing at the pressure of, e.g., 0.5 MPa are measured.

FIGS. 4 and 5 are graphs showing results of the measurements.

As can be seen from the graph of FIG. 4, the impregnation time issuddenly lengthened when the amount of additional polyvinyl alcoholexceeds 5 wt %. This is because the polyvinyl alcohol forms a filmbarrier and inhibits the impregnating resin from being impregnated.

As can be seen from the graph of FIG. 5, when the amount of additionalpolyvinyl alcohol is not larger than 0.5 wt %, the inorganic particles14 flow out of the insulation wall 8 with heat pressing at the formationof the insulation wall 8. Therefore, the thermal conductivity cannot beimproved as is expected.

Consequently, polyvinyl alcohol is added favorably in an additionalamount between 0.5 wt % and 5 wt % as glue included in the adhesive 13,and the inorganic particles 14 are supported with the mica tape 71. Theabove amount of additional polyvinyl alcohol and the supporting effectthereof exclude the influence of a long-time resin impregnation, and theinorganic particles 14 can be prevented from flowing out of theinsulation layer 8; therefore, the thermal conductivity can be improved.

According to the first embodiment, the supporting effect of polyvinylalcohol prevents the flowing out of the inorganic particles 14 withimpregnated resin from the insulation wall 8 even when the heat pressingis applied to form a final section.

Hence, the thermal conductivity of the insulation wall 8 is improved andsecondarily the falling of the inorganic particles 14 when the mica tapeis wound can be decreased. Since, furthermore, the polyvinyl alcohol isadded in an appropriate amount, the influence of a long-timeimpregnation can be lessened.

If, moreover, the stator that is accommodated the coil in a slot, thethermal conductivity of a heat pass from the conductor to the coolinggas is increased, so that the temperature rise of the stator coil can bedecreased and the machine can be decreased in size.

A second embodiment will now be explained.

In the second embodiment, an adhesive 13 containing, for example, 3 wt %of polyvinyl butyral, which is a kind of polyvinyl acetal, is used as apolyvinyl-based polymer that is an indispensable component as glue. Anuncalcinated muscovite mica tape 71 with the adhesive 13 is wound aplurality of layers around a conductor 22. The uncalcinated muscovitemica tape 71 is formed with supporting inorganic particles 14 of boronnitride particles on a glass cloth backing 6.

As the adhesive 13, an epoxy resin composition (for example, Epikote 828or 1001 manufactured by Yuka-Shell Co., Ltd.) is used in addition topolyvinyl butyral.

After a thermosetting resin is impregnated, the wound layers of the micatape 71 under vacuum pressurized condition is heated and cured by heatpressing at a pressure of, e.g., 0.5 MPa while a stator coil 2 is formedto a final section. An insulation wall 8 is formed on the periphery ofthe conduct 22 due to the heating and curing of the thermosetting resinin mica tape 71.

Favorably, the impregnating resin is a composition comprising a 45 wt %of cycloaliphatic epoxy compound, a 40 wt % of acid anhydride curingagent, and a 15 wt % of reactive diluent as disclosed in Jpn. Pat.Appln. KOKAI Publication 11-345733. This impregnating resin has a lowviscosity of about 30 mPa·s at room temperature.

The second embodiment can also attain the same advantage as that of thefirst embodiment.

A third embodiment will be described below.

According to the third embodiment, an adhesive 13 containing, forexample, 3 wt % of polyvinyl formal, which is a kind of polyvinylacetal, is used as a polyvinyl-based polymer that is an indispensablecomponent as glue. A uncalcinated muscovite mica tape 71 with theadhesive 13 is wound a plurality of layers around a conductor 22. Theuncalcinated muscovite mica tape 71 is formed with supporting inorganicparticles 14 of aluminum nitride particles on a glass cloth backing 6.

As the above adhesive 13, an epoxy resin composition (for example,Epikote 828 or 1001 manufactured by Yuka-Shell Co., Ltd.) is used inaddition to polyvinyl formal.

After a thermosetting resin is impregnated into the wound layers of themica tape 71 under vacuum pressurized condition, it is heated and curedwith heat pressing at a pressure of 0.5 MPa while a stator coil 2 isformed so as to have a final section. Due to the heating and curing ofthe thermosetting resin and mica tape 71, an insulation layer 8 isformed on the periphery of the conductor 22.

Favorably, the impregnating resin is a composition comprising a 45 wt %of cycloaliphatic epoxy compound, a 40 wt % of acid anhydride curingagent, and a 15 wt % of reactive diluent as in the second embodiment.This impregnating resin has a low viscosity of about 30 mPa·s at roomtemperature.

The third embodiment can also attain the same advantage as that of thefirst embodiment.

In the first to third embodiments, aluminum oxide (Al₂O₃), boron nitride(BN), or aluminum nitride (AlN) is used as the inorganic particles 14.In addition to Al₂O₃, BN and AlN, at least one or two or more ofberyllium oxide (BeO), magnesium oxide (MgO) and silicon carbide (SiC)can be used as the inorganic particles 14.

Furthermore, one of polyvinyl alcohol, polyvinyl butyral and polyvinylformal is used as glue contained in the adhesive. At least two ofpolyvinyl alcohol, polyvinyl butyral and polyvinyl formal can be used asthe glue. In either case, a polyvinyl-based polymer is used as the glue.

The mica tape 71 is not limited to the first to third embodiments.Needless to say, the mica tape 71 can be applied to the insulation for arotator coil of an electric rotating machine.

The mica tape 71 also includes a mica sheet 72 that is formed like asheet.

As has been described above, the high thermal-conductivity inorganicparticles 14 are arranged on the mica tape 71 (mica sheet 72) andsupported on the mica tape 71 (72) using the adhesive 13 containing glueinsoluble in the impregnating resin. Therefore, the inorganic particles14 do not flow out, by virtue of the supporting effect of the glue, evenin the process of squeezing the impregnated resin with heat pressing andthen forming the insulation wall 8 to a final section. Consequently, theeffect of improving the thermal conductivity of the insulation wall 8 isconspicuous and the influence of the glue on the impregnating time canbe lessened.

In the mica tape 71 (mica sheet 72) of the above embodiments, thebacking base material combined with the mica paper 5 is not limited tothe glass cloth backing 6. A cloth-like base material, such as polyestercloth, aramid cloth and alumina cloth has only to be used as the backingbase material of the mica tape 71 (mica sheet 72).

A high-efficiency electric rotating machine is achieved with a statorcoil that is sufficiently improved in thermal conductivity.

1. A coil for an electric rotating machine, comprising: a conductorconfigured by bundling a plurality of square strands and stacking thesquare strands like a coil with Roebel transposition; mica tape which iswound a plurality of layers around on surface of the conductor and madeup of mica paper and cloth backing material; an insulation layer formedwith impregnating and curing resin between wound layers of the micatape; and inorganic particles supported with the mica tape using anadhesive comprising a first component having mutual dissolubility withthe impregnating resin and a second glue component insoluble in theimpregnating resin, the second glue provided in an amount sufficientlysmall so as not to inhibit impregnation of impregnating resin, yetsufficiently large so as to impede outflow of said inorganic particles.2. A coil for an electric rotating machine, comprising: a conductorconfigured by bundling a plurality of square strands and stacking thesquare strands like a coil with Roebel transposition; mica tape which iswound a plurality of layers around an outer surface of the conductor andmade up of mica paper and cloth backing material; an insulation layerformed by impregnating and curing resin between wound layers of the micatape; and inorganic particles supported with the cloth backing materialof the mica tape using an adhesive comprising a first component havingmutual dissolubility with the impregnating resin and a second gluecomponent insoluble in the impregnating resin, the second glue providedin an amount sufficiently small so as not to inhibit impregnation ofimpregnating resin, yet sufficiently large so as to impede outflow ofsaid inorganic particle.
 3. The coil for an electric rotating machineaccording to one of claims 1 or 2, wherein the inorganic particlesinclude at least one of aluminum oxide (Al2O3), beryllium oxide (BeO),magnesium oxide (MgO), aluminum nitride (AlN), boron nitride (BN), andsilicon carbide (SiC).
 4. The coil for an electric rotating machineaccording to one of claims 1 or 2, wherein the second glue componentcontained in the adhesive is polyvinyl alcohol.
 5. The coil for anelectric rotating machine according to one of claims 1 or 2, wherein thesecond glue component contained in the adhesive is polyvinyl acetal. 6.The coil for an electric rotating machine according to one of claims 1or 2, wherein the second glue component contained in the adhesiveincludes at least one of polyvinyl alcohol and polyvinyl acetal.
 7. Thecoil for an electric rotating machine according to one of claims 1 or 2,wherein the second glue component contained in the adhesive is apolyvinyl-based polymer.
 8. Mica tape used for insulating a coil of anelectric rotating machine, comprising: mica paper; glass cloth backingof the mica paper; and inorganic particles supported by the glass clothbacking using an adhesive containing a first component having mutualdissolubility with an impregnating resin and a second glue componentinsoluble in the impregnating resin, the second glue provided in anamount sufficiently small so as not to inhibit impregnation ofimpregnating resin, yet sufficiently large so as to impede outflow ofsaid inorganic particle.
 9. The mica tape according to claim 8, whereinthe second glue component of the adhesive is a polyvinyl-based polymer,and the inorganic particles are aluminum oxide particles.
 10. The micatape according to claim 8, wherein the second glue component of theadhesive is a polyvinyl-based polymer, and the inorganic particles areboron nitride particles.
 11. A mica sheet used for insulating a coil ofan electric rotating machine, comprising: mica paper; glass clothbacking of the mica paper; and inorganic particles supported by theglass cloth backing using an adhesive containing a first componenthaving mutual dissolubility with an impregnating resin and a second gluecomponent insoluble in the impregnating resin, the second glue providedin an amount sufficiently small so as not to inhibit impregnation ofimpregnating resin, yet sufficiently large so as to impede outflow ofsaid inorganic particle.
 12. The mica sheet according to claim 11,wherein the second glue component of the adhesive is a polyvinyl-basedpolymer, and the inorganic particles are aluminum oxide particles. 13.The mica sheet according to claim 11, wherein the second glue componentof the adhesive is a polyvinyl-based polymer, and the inorganicparticles are boron nitride particles.